Television system and scanning apparatus



- l. S. MITCHELL TELEVISION SYSTEM AND SCANNING APPARATUS June 24-,

Filed Feb. 9, 1938 2 Sheets-Sheet 1 INVENTOR. 0W7? Smf/h MVchefl June 24, 1941. s rj- 2,247,030

TELEVISION SYSTEM AND- SCANNING APPARATUS Filed Feb. 9, 1938 2 Sheets-Sheet 2 [Ill v2 I ATTORNEY.

Patented June 24, 1941 UNETED STATES. PATENT OFFICE TELEVISION SYSTEM AND SCANNING APPARATUS This invention relates to television and is concerned both with a system of television taken as an entirety and particularly with the scanning apparatus employed in television systems.

Modern development work in the field of television has resulted in the evolution of various systems of picture transmission either wire or wireless, all of which may be characterized as including the scanning of a picture and throwing the light rays resulting from the scanning onto a photo-electric cell to produce a variable electric current. This variable electric current is transmitted either by wires or radio, and at the receiving end is taken as the controlling element for a variable light source the light beam from which is projected by mechanism comparable to the scanning apparatus onto a screen to produce an image.

At the present time the factor which is perhaps causing the greatest trouble in the field of television is that synchrony between the scanning apparatus in the transmitting set and the corresponding mechanism in the receiving set. It is well recognized in this art that the definition of any picture transmitted is intimately tied up with this synchrony factor, and this is true whether the scanning be carried out by purely mechani cal apparatus or by cathode ray tubes.

With the foregoing conditions in mind this invention has in view as an important objective the provision of a novel television system in which perfect synchrony between the scanning apparatus in the transmitting set and the corresponding mechanism in the receiving set is insured.

In attaining this objective the invention contemplates the use of a central broadcasting station which is intended to broadcast a tone signal which constitutes the controlling element in the operation of the scanning apparatus at the transmitting set and the corresponding mechanism at the receiving station.

A further detailed object of the invention is the provision of a television system including a central station which is equipped to transmit two tone signals of widely varying audio frequencies. Generally speaking the scanning of a picture or scene is broken up into vertical and horizontal movements, and the projection of a light beam to reproduce the image involves corresponding movements.

Hence the tone signal on one frequency which is produced from one station is designed to control either the vertical or horizontal movements at both the transmitting and receiving stations,

while the tone signal on the other frequency is intended to be controlling of the other movement.

The invention has in View as another highly important object the provision, in a television system, of novel and improved scanning apparatus which is peculiarly adapted for use in a system involving the broadcasting of tone signals from a central station in the manner above indicated. More in detail the invention has in mind the provision of scanning apparatus of the vibratory type with the vibrations accurately controlled by the tone signals broadcast from the central station.

A further more particular object of the invention is the provision of mechanism which intended to constitute either the scanning apparatus at the transmitting station or the corresponding mechanism for projecting a light beam at the receiving station, and which mechanism provides for the vertical and horizontal oscillation of an aperture through which a light beam is adapted to pass. The aperture is formed in a plate, and appropriate mechanical means are employed in the mounting of the plate to provide for the vertical and horizontal oscillatory vibrations under the influence of solenoids. The solenoids are rendered effective by electrical currents which result from the amplifying of the tone signals that are picked up from the central station.

Various other more detailed objects and advantages such as arise from the carrying out of the above noted objects in a practical embodiment will in part become apparent and in part be hereinafter stated, as the description of the invention proceeds.

The invention, therefore, comprises a television system Which is characterized as including, in addition to the usual transmitting and receiving stations, a central station for broadcasting a pair of tone signals of different audio frequencies and which tone signals are intended to control the operation of the scanning apparatus at the transmitting station and the corresponding mechanism at the receiving station. Highly important parts of the invention are the duplicate mechanisms employed at the transmitting and receivirig stations respectively, each of which mechanisms involves the vertical and horizontal oscillatory vibration of an aperture through which a light beam passes, together with the apparatus for causing such oscillatory vibrations under the influence of the tone signals broadcast from the central station.

For a full and more complete understanding of the invention reference may be had to the following description and accompanying drawings, wherein Figure 1 is a diagrammatic representation of a television system embodying the precepts of this invention,

Figure 2 is a perspective view with parts removed of the mechanism employed as a scanner at the transmitting station, and for controlling the projection of a light beam at the receiving station,

Figure 3 is a vertical section through the casing including the mechanism shown in Figure 2. This view is taken as a side view of the mechanism itself, I

Figure 4 is a top plan view of the mechanism with the walls of the casing shown in section, and

Figure 5 is a detailed plan view of one of the solenoids and the armature associated therewith.

In the following description the invention is described as designed for use in the wireless or radio picture transmission. However, it is to be clearly understood that the invention is equally adaptable for use in the wired transmission of pictures.

Referring now to the drawings, and more particularly Figure l, a transmitting station is identified in its entirety by the reference character T, while a receiving station is referred to as R.

A central broadcasting station is indicated at C.

The transmitting station T includes scanning apparatus which is referred to in its entirety by the reference character It. This scanning apparatus includes a pair of solenoids represented diagrammatically at II and i2, respectively. One of these solenoids is intended to provide for the vertical oscillation of an aperture I3 included in the scanning mechanism 89 in a manner to be hereinafter described in detail, while the other solenoid provides for the horizontal oscillation of the aperture is. These solenoids II and 52 are connected with radio receiving apparatus M, which is intended to pick up tone signals on different audio frequencies which are broadcast from the central station C, and amplify these signals into current sufficiently strong to operate the solenoids II and I2.

Inasmuch as the amplification of electrical signals in this manner is now a matter well-known to those skilled in the radio art, it is not deemed necessary to here illustrate or describe the receiving apparatus which is employed for that purpose.

A scene or image which is to be transmitted is represented at I5. This image I5 is scanned by the vertical and horizontal oscillation of the aperture i3 in the scanning apparatus. The light beam passing through this aperture strikes a photo-electric cell represented at I6, to vary the electrical current passing therethrough in accordance with the intensity of the light beam as determined by the light and dark values of the image I5. 1

This variable electrical current which passes through the photo-electric cell It is delivered by the electrical circuit I! to radio transmitting mechanism it that amplifies the current and broadcasts the same, as represented by the aerial at IS.

The current which is broadcast from the apparatus I3 of the transmitting station T may be picked up by one or more of the receiving stations B. Each of the receiving stations R. will include radio receiving mechanism for picking up the variable electric current broadcast from the apparatus IS. The receiving mechanism 20 will in- CFI elude suitable means of amplification for delivering current of a required strength to a light source which preferably takes the form of a glow discharge tube represented at 2|.

Associated with the tube 2| are suitable optical instrumentalities designated 22 for condensing the light coming from the tube 2I and throwing the same as a beam against the plate 23 formed with an aperture 24, The plate 23 is part of mechanism that is the mechanical duplicate of the mechanism IE1 at the transmitting station T, and associated therewith are solenoids 25 and 26 for causing the vertical and horizontal vibration of the aperture 24, and these solenoids are operated under the influence of electrical currents that result from the amplification of tone signals broadcast from the central station C, and picked up and amplified by the radio receiving mechanism 21.

The light beam from the glow discharge tube 2I passes through the aperture 24 and through additional optical instrumentalities at 28 from which it is projected on a screen 29 to form the image which is the replica of the scene or image at I 5.

Each of the receiving sets I4 and 21 preferably includes a wellknown type of variable impedance choke so that the current supplied to the several solenoids may be varied as occasion demands. Ordinarily this impedance will be included in the last stage of amplification at each station.

From the foregoing description it is evident that oscillations of the apertures I3 and 24 respectively will be in exact and perfect synchrony, as the vibratory movements are caused by soleoids that are operated under the influence of the same tone signals broadcast from the central station C.

Referring now more particularly to Figures 2 to 5, inclusive, the mechanism which constitutes the scanning apparatus in the transmitting station T, and the mechanism for providing the vibrating aperture 24 at the receiving station R will now be described.

At the transmitting station there will be employed a casing 30 such as shown in Figures 3 and 4, and which casing will be formed with a window or opening at 3| through which light rays from the scene or image I5 may pass. Mounted adjacent the rear wall 32 of the casing 30 is the photo-electric cell I6 which is connected by the wires I I to the transmitting apparatus I 8.

Mounted on vertical pivot points 33 and 34 is a frame 35, and this frame at its lower extremity carries a rearwardly projecting arm 36 that carries an armature 31 that is adapted for cooperation with the solenoid II to cause horizontal vibratory movement of the frame 35 on the pivot points 33 and 34.

As above pointed out, the solenoid II is conductively connected with the radio receiving apparatus I4 by wires represented at 38. A spring 39 is intended to cooperate with the solenoids II in a well-known manner to draw the armature away therefrom when the magnetic field of the solenoid H is broken.

Mounted on the horizontal pivot points 40 and M in the frame 35 is a plate 42 that is formed with the aperture I3. It is particularly important to note that the aperture I3 is eccentric to the axis defined by the pivots 49 and 4|, and also eccentrio to the axis defined by the pivot points 33 and 34.

Projecting below the axis defined by the pivot points 48 and 4| is an arm 43 that carries an armature 44. Cooperating with the armature 44 is the solenoid i2 that is connected by the wires 55 with the radio receiving apparatus it.

As shown in Figure 5, the nose of the solenoid i2 is of arcuate formation as represented at 46, and the nose of the armature M is complementally shaped. Thus when the armature engages the nose of the solenoid 4-5 horizontal vibration under the influence of the solenoid i l is permitted, due to this curvature.

A bracket ll is carried by the frame 35, and interposed between this bracket i? and the plate #32 is a spring i8 that is comparable to the spring 39. This spring .18 normally exerts a tendency drawing the armature id away from the solenoid 2. The limit of movement in this direction may be determined by a set screw at 6d, and a similar set screw is shown at i? as mounted on a bracket M for limiting horizontal vibratory movement.

The mechanism illustrated in Figures 2 to 5, inclusive, and above described is shown as particularly designed for the transmitting station T. However, the same mechanical parts and set up is availed of to provide the mechanism for controlling the projection of the light beam at the receiving station R; the plate 23 and aperture 2d being the exact counterparts of the plate i2 and aperture l3. However, at the receiving station R the photo-electric cell it is replaced by the glow discharge tube 2! and associated optical instrumentalities.

It is important to note that the tone signals which operate the solenoids H and 25 for causing the vertical vibrations are of high audio frequency, thus providing for a comparatively large number of vertical vibrations. On the other hand the tone signal for operating the solenoids l2 and 2% for causing the horizontal vibrations is relatively low, providing for a comparatively few number of horizontal vibrations. This differential is important in the scanning of an image. At the same time it insures of broadcasting of the tone signals on different audio frequencies without interference, thus rendering the vertical and horizontal vibratory movements independent.

In the form of the invention illustrated in the drawings and above described the scene or image i5 is shown as being scanned directly by the aperture E3 in the piate i2. In this connection it is notable that suitable optical instrumentalities may be associated with the aperture in any wellknown manner.

While a preferred specific embodiment of the invention is hereinbefore set forth it is to be clearly understood that I am not to be limited to the exact construction illustrated and described, because various modifications of these details may be provided in putting the invention into practice within the purview of the appended claims.

I claim:

1. In television, mechanism adapted to constitute either the scanning apparatus at a transmitting station or mechanism for projecting a light beam at a receiving station comprising a plate formed with a scanning aperture, said plate being mounted for oscillation on a vertical axis that is out of alignment with said aperture, said plate also being mounted for vibratory movement on a horizontal axis that is out of alignment with said aperture, means for causing horizontal vibratory movements of said plate, and independent means for causing vertical vibratory movements.

2. In television, mechanism adapted to constitute either the scanning apparatus at a transmitting station or mechanism for projecting a light beam at a receiving station comprising a frame ivotally mounted for oscillatory movement on an axis, a plate pivotally mounted in said frame for oscillatory movement on an axis normal to the axis of the pivotal mounting of the frame, said plate being formed with a scanning aperture cut of alignment with each of said axes, a solenoid associated with the frame for causing oscillatory movement thereof, and a second solenoid associated with the plate for causing oscillatory movement thereof.

3. In television, mechanism adapted to constitute either the scanning apparatus at a transmitting station or mechanism for projecting a light beam at a receiving station comprising a frame pivotally mounted for oscillatory movement on an axis, a plate pivotally mounted in said frame for oscillatory movement on an axis normal to the axis of the pivotal mounting of the frame, said plate being formed with a scanning aperture out of alignment with each of said axes, an arm extending from said frame, a solenoid disposed on one side of said arm, and a spring disposed on the other side of said arm, said spring and solenoid cooperating to cause vibratory oscillation of said frame, a second solenoid disposed on one side of said plate, and a spring on the other side of the plate cooperating with the solenoid for causing vibration of the plate with respect to the frame.

4. In television, mechanism designed to constitute scanning apparatus at a transmitting station or mechanism for projecting a light beam at a receiving station, said mechanism comprising a frame mounted on vertically disposed pivotal points to provide for horizontal vibratory oscillation of said frame, an arm projecting from said frame and carrying an armature, a solenoid associated with the armature, and a spring on the side of the arm opposite the armature, said spring and solenoid cooperating to cause horizontal vibratory oscillation of the frame, a plate mounted on horizontally disposed pivot points in said frame to provide for vertical oscillation of said plate with respect to the frame, said plate being formed with a scanning aperture that is out of alignment of both of the axes defined by said vertical and horizontal pivot points, said plate being formed with an extension below said horizontal pivot points, an armature carried by said extension, a solenoid associated with the armature, and a spring cooperating with the solenoid to cause the vertical vibratory oscillations of said plate.

IRVIN SMITH MITCHELL. 

